ATSC Updates CALM Act’s TV Loudness Recommended Practice

ATSC has delivered an updated version of ATSC A/85, the core technology mandated by the Commercial Advertisement Loudness Mitigation (CALM) Act, to the Federal Communications Commission (FCC).

The A/85 Recommended Practice (Techniques for Establishing and Maintaining Audio Loudness for Digital Television) provides the industry with uniform operating strategies that optimize the audience listening experience by eliminating wide variation of television loudness. The ATSC, which optimized A/85 based upon industry experience and feedback is fortunate to have industry experts from our member organizations participate in this important work.

As approved by ATSC members, the revised version of A/85 includes an update of the reference to the International Telecommunications Union (ITU) recommendation for “algorithms to measure audio programme loudness and true-peak audio level.”

The revised A/85 now references ITU-R BS.1770-3. Version 3 of BS.1770, adds “gating” (excluding low level passages from the measured value) to the measurement algorithm.

In addition, version 3 of BS.1770 includes some minor editorial updates to the loudness measurement text and a minor correction to the true-peak measurement algorithm.

Beyond the reference change, A/85 now includes improved guidance for measuring the loudness of surround programming in both its multichannel format and in its 2-channel downmix. This is important because many consumers utilize the stereo downmix of surround programming and it is possible to have loudness disparity between the two modes.

In addition, A/85 is now specific about the differences between loudness and dynamic range.